This invention relates to liquid ring pumps, and more particularly to controlling the flow of seal liquid injection into the xe2x80x9csweepxe2x80x9d portion of such pumps.
Liquid ring pumps are well known, as is shown, for example, by Adams U.S. Pat. No. 3,289,918 (which is hereby incorporated by reference herein in its entirety). The Adams patent shows that it is known that the compression ratio of a liquid ring pump can be increased by injecting additional seal liquid into the liquid ring in the pump at an appropriate location between the gas intake and gas discharge of the pump (i.e., in the so-called xe2x80x9csweepxe2x80x9d of the pump). However, the known means for introducing such pressurized seal liquid tend to have fixed flow characteristics. This can be a disadvantage when certain operating conditions of the pump change and/or when certain changes are made in the operating configuration of the pump.
In view of the foregoing, it is an object of this invention to provide improved liquid ring pumps.
It is a more particular object of the invention to provide liquid ring pumps with improved seal liquid injection arrangements.
These and other objects of the invention are accomplished in accordance with the principles of the invention by providing liquid ring pumps with seal liquid injection that is actively controlled based on at least one operating parameter of the pump. For example, the seal liquid may be supplied from a pressurized source via a variable flow control valve. At least one operating condition of the pump (e.g., seal liquid injection pressure) is monitored to provide information for controlling the amount by which the variable flow control valve is opened. Valve control structure is provided for using that information to open the valve by an amount appropriate to the current pump operating condition information. For example, if seal liquid injection pressure is the pump operating condition being monitored, the seal liquid flow control valve may be controlled to maintain a desired seal liquid injection pressure. Other examples of pump operating conditions or parameters that may be monitored in order to provide alternative or additional information for control of the seal liquid flow control valve include pump speed, gas inlet pressure and/or temperature, and gas discharge pressure and/or temperature. Control may be based on monitoring multiple operating parameters. For example, both gas inlet pressure and gas discharge pressure may be monitored to allow control to be based on the gas pressure differential at which the pump is operating. In that example, the seal liquid flow control valve may be controlled to be closed or open relatively little when the gas pressure differential is low, and to be open to a greater degree when the gas pressure differential is higher.
Among the advantages of using the present invention are that it helps to prevent liquid ring pumps from stalling, and that it otherwise improves the operating stability of such pumps. It also facilitates the use of external seal liquid sources. Such sources tend to have a constant pressure, which can be too high for the liquid ring pumps under some operating conditions, such as during start-up. However, because the present invention provides for active control of the pressure of seal liquid injected into the pump, a seal liquid source having a constant pressure can now be used without difficulty.
Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments.